A semiconductor injection laser comprises a body of semiconductor material, generally a group III-V compound or alloys of such compounds, having a thin active layer between layers of opposite conductivity type, that is, a layer of P-type conductivity on one side of the active layer and a region of N-type conductivity on the other side of the active layer. These layers are typically deposited by liquid phase epitaxy, as is well known. If the surface of a substrate upon which these layers are grown is perturbed, for example, by grooves extending into the surface of the substrate, the layers may be grown with varying thicknesses. These variations arise from the fact that in liquid phase epitaxy the local deposition rate will vary with surface curvature, the greater the local concavity of the surface, the faster the deposition rate.
Botez, in U.S. Pat. No. 4,347,486 filed Apr. 6, 1981 which is a continuation-in-part of U.S. application Ser. No. 84,347 filed Oct. 12, 1979, now abandoned, and entitled "Single Filament Semiconductor Laser with Large Emitting Area," which is incorporated herein by reference, has disclosed a semiconductor laser, known as a CDH-LOC laser, which comprises a body of semiconductor material having a substrate with a pair of spaced, substantially parallel grooves in its surface. A first confinement layer overlies the surface of the substrate and the surfaces of the grooves. A guide layer overlies the first confinement layer and an active layer overlies the first confinement layer. A second confinement layer overlies the active layer. The guide layer has an index of refraction less than that of the active layer but larger than that of either the first or second confinement layers. The substrate, the first confinement layer and the guide layer are of the same conductivity type and the second confinement layer is of the opposite conductivity type. The active layer is the recombination region of the laser. The light beam is generated therein in the portion which is over that part of the substrate between the grooves. The light beam so generated propagates in both the thin active region and, primarily, in the relatively thicker guide layer, thereby forming a laser filament having a large cross-sectional area. This laser also has excellent selectivity against higher order modes of propagation of the generated laser beam since the waveguide formed by the active and guide layers in the lateral direction (the direction in the plane of the layers and perpendicular to the axes of the grooves) exhibits high loss for these modes but has the disadvantages that both the threshold current for lasing action and the spontaneous emission near threshold are higher than is desireable. It would be advantageous to have a CDH-LOC laser which reduced these undesired properties.